Patent GB-906918-A (GB)
Title: Storing and reproducing coordinate functions
IPC: G01V1/24
Filed: 1960-02-02
Abstract: 906,918. Geophysical prospecting. ATLANTIC REFINING CO. Feb. 2, 1960 [Feb. 2, 1959], No. 3654/60. Class 40 (7). In apparatus for recording a coordinate function on a ferromagnetic medium moving relative to a recording transducer the magnetization of the medium is varied at points thereon when the function ordinate or slope changes by a predetermined amount; and in apparatus for reproduction from the medium, means sequentially count pulses from a receiving transducer moving relative to the medium and further means convert the counted pulses into a digital output or into a voltage analogous to the original function. The invention is described as applied to the correction of seismic records for dynamic and static errors. Fig. 1 represents a typical record of the outputs of geophones a, b, c, geophone a being assumed to be 2X feet from the shot point, b at X feet and c adjacent thereto, and the desired form, free from those errors, is depicted in Fig. 3. Since all corrections are by time delays, an inverted form, Fig. 4, of correction curve is employed and the corresponding static and dynamic error components are represented on magnetic tracks, Fig. 5, as shown. For the storage and reproduction of non- monotonic functions the means adopted on the magnetic tape to indicate a change of sign in slope of the function may be a transverselydisplaced spot of magnetization at the sign change, Fig. 6a (not shown), or a transverselydisplaced spot row during the reverse slope of the function, Fig. 6b (not shown); or the frequency of an oscillator is changed whenever the slope of assumed straight-line segments approximating the function occur, Figs. 7a, 7b (neither shown) and the oscillator output is converted to a plurality of pulses by a conventional voltage discriminator, the output from which is applied to a recording head to place on the tape a plurality of magnetic spots equal in number to the number of pulses produced by the voltage discriminator and whose repetition rate is thus proportional to the frequency of the oscillator and represents the slope of a particular segment of the function. In an embodiment for preparing the tape programme depicted in Fig. 5 a recording head 3, Fig. 9, is fixed relative to rotating tape drum 1 and fed from a power source by manual switch 5, and a mechanical totalizing counter 15 coordinated with the time scale along the tape on the drum is coupled to the drum. For programming non-monotonic functions a second head 19 is mounted to record a second information track and third contacts are added to switches 5, 17. An erase circuit may be included, Fig. 10 (not shown). In a preferred arrangement of counter 15 the latter is provided with a spring-loaded reset knob 31, Figs. 11 and 12, normally biased out of engagement with the numbered discs of the counter. Knob 33 is connected to the extension of the tape drum shaft and carries gear 35 for manual " inching " of the drum, the counter then being actuated via idler gear 37, gear 39 and bevel gears 41. To prevent counter actuation when the driving motor is turning, the counter and gears 37, 39, 41 are mounted on a sector 43 pivoted at 45; if the drum motor is switched on, a solenoid 47 is actuated, thus turning sector 43 on the pivot to rock gear 37 out of engagement with gear 35; at the same time pawl 49 holds the sector in that position with gears 35, 37 out of engagement, and micro-switch 51 is disengaged, breaking the circuit to the solenoid to prevent overheating thereof. Re-engagement of the counter with the tape drum shaft is attained by releasing pawl 49 by pushing button 53. For reading out from the tape, two heads, multivibrators for sharpening the pulse outputs, a reversing counter and digital-toanalogue converters whose outputs are combined, are provided; arrangements are included for reading out from non-monotonic function records, Fig. 15 (not shown). A reversing counter described employs known beam switching valves of the type comprising ten arrays, each of which includes a spade electrode for forming and locking an electron beam, located radially about a central cathode, and incorporating a cylindrical magnet permanently attached to the glass envelope of the valve, Fig. 16 (not shown).